The present invention relates to a locking screw.
Closing screws for connecting closing lugs generally comprise a head, which bears on or is countersunk in a first closing lug, a neck, which extends through the first closing lug, and a screw-threaded shank, which is screwed in the second closing lug. It has been suggested to provide plastic extrusions in longitudinal grooves formed adjacent to the screw threads of the shank of the locking screw so that the plastic extrusions cooperate with the female screw threads in the second closing lug to lock the screw. After some joining and separating operations, however, the screw threads often destroy the plastic extrusions. In the manufacture of eyeglass frames, for example, and more specifically during the mounting of the lens in the frame, it is necessary to separate and join the closing lugs of the metal rims several times. This action will soon result in destruction of the plastic extrusions which have been inserted into longitudinal grooves of the screw-threaded shanks of the locking screws.
Published German Application 33 35 046 discloses locking screws in combination with small plastic cleats, which are inserted into and anchored in the female screw threads of a second closing lug so that the plastic cleats cooperate with the male screw threads of the shank of the locking screw to lock the latter. The resulting joint, however, will often suffer from the disadvantages outlined above. German Utility Model 88 15 277 discloses a locking screw which is provided under its head with a plastic ring, which cooperates with an annular series of teeth formed in the recess in which the head of the locking screw is received in the first closing lug. The plastic ring will also be destroyed or worn out after several separating operations.
It is, therefore, an object of the present invention to provide a novel locking screw which ensures that there will be virtually no wear at the joint between the closing lugs even after the joint has been separated and restored several times.
The object is accomplished in accordance with the invention by a locking screw having a neck, which is recessed from the shank and surrounded by a plastic ring. The ring may be injection-molded in situ and protrudes from the shank and adjoins an unthreaded portion of the shank. The plastic ring is arranged to frictionally engage an unthreaded through bore of the first closing lug as the locking screw is screwed into the female screw threads of the second closing lug.